Cobalt (Co)
Cobalt (Co) is a chemical element with the atomic number 27, belonging to the transition metals group of the periodic table. It is recognized for its lustrous, silvery-blue appearance and is found in various ores, primarily in the Democratic Republic of the Congo, Australia, Canada, Zambia, Russia, and Cuba. Cobalt has important industrial applications, with the largest use being in superalloys, which are designed for high-stress and high-temperature environments. It is also utilized in magnetic alloys, cemented carbides, and as a pigment in ceramics and glass.
Cobalt's properties include a density of 8.90 grams per cubic centimeter, a melting point of 1,495° Celsius, and a boiling point of 3,100° Celsius. It exists in multiple oxidation states and forms vibrant compounds, contributing to its historical use in art and glassmaking dating back to ancient civilizations. While cobalt is essential for certain animals in trace amounts, excessive exposure can be harmful. In humans, it plays a critical role as a component of vitamin B12, with deficiencies leading to serious health issues. Overall, cobalt is a versatile element with significant implications across various industries and biological contexts.
Cobalt (Co)
Where Found
Cobalt is widely distributed in the Earth’s crust in many ores, but only a few are of commercial value; the most important of these are arsenides and sulfides. The world’s major sources are in the Democratic Republic of the Congo, Australia, Canada, Zambia, Russia, and Cuba.
Primary Uses
The largest use of cobalt is in superalloys, alloys designed to resist stress and corrosion at high temperatures. Other important uses are in magnetic alloys for motors, meters, and electronics and as a binder in cemented carbides and diamond tools.
Technical Definition
Cobalt (abbreviated Co), atomic number 27, belongs to Group VIII of the transition elements of the periodic table and resembles iron and nickel in many chemical and physical properties. It has one naturally occurring isotope, with an atomic weight of 58.194. Cobalt as a metal is lustrous and silvery with a bluish tinge. It has an allotropic form that is stable only above 417° Celsius. Its density is 8.90 grams per cubic centimeter; it has a melting point of 1,495° Celsius and a boiling point of 3,100° Celsius. Cobalt is known to exist in more than two hundred ores. These are invariably associated with nickel and often also with copper and lead. Cobalt is tougher, stronger, and harder than nickel and iron although less hard than iridium and rhodium. It is ferromagnetic at less than 1,000° Celsius. Like other transition elements, it has multiple oxidation states (II and III are most common), forms coordination complexes, and produces several colorful compounds and solutions.
Description, Distribution, and Forms
Cobalt is about 29 parts per million of the Earth’s crust, making it the thirtieth element in order of abundance. It is less abundant than the other first-row transition elements except scandium. Other than the reserves of cobalt in Africa and Canada, there are smaller reserves in Australia and in Russia. In 2006, for example, the leading producers of cobalt ore were the Democratic Republic of the Congo (41 percent), Zambia (12 percent), Australia (11 percent), Canada (10 percent), Russia (8 percent), Cuba (6 percent), and China (3 percent). Total world production was about 67,500 metric tons.
Studies have shown that land with a cobalt deficiency will cause ruminant animals to lose their appetite, lose weight, and finally die; the disease is essentially a vitamin B12 deficiency. Vitamin B12 is necessary in ruminants for metabolism. In other animals cobalt does not seem to be essential. However, humans do need vitamin B12, also called cyanocobalamine; in humans a B12 deficiency causes megaloblastic anemia.
Cobalt appears in many materials, including soils and water. There is evidence that minute quantities can be harmful to higher plant life. It can also be harmful to animals; for example, sheep are harmed if they consume more than 160 milligrams of cobalt per 45 kilograms of weight. There is no evidence that the normal human level of exposure to cobalt is harmful.
History
Egyptian pottery from 2600 b.c.e., Iranian glass from 2250 b.c.e., and Egyptian and Babylonian blue glass from 1400 b.c.e. owe their blue color to cobalt. Apparently, however, the art of making blue glass from cobalt ores disappeared until the end of the fifteenth century, when Christoph Schiirer used cobalt ores to impart a deep blue color to glass. Cobalt ores were used not only to color glass but also as a blue paint for glass vessels and on canvas. In 1735, Swedish chemist Georg Brandt recognized the source of the color and is considered the discoverer of cobalt. In 1780, Torbern Olaf Bergman showed it to be a new element. Although the name is close to the Greek cobalos, for mine, the word cobalt is thought to come from the German word Kobald, for goblin or evil spirit. Miners called certain ores kobald because they did not produce copper but did produce arsenic compounds that were harmful to those near the smelting process.
Obtaining Cobalt
Cobalt is usually produced as a by-product of copper, nickel, or lead, and the extraction method depends on the main product. In general, the ore is roasted to remove gangue material as slag and produce a mixture of metals and oxides. The copper is removed with sulfuric acid. The iron is precipitated with lime, and sodium hypochlorite precipitates the cobalt as a hydroxide, which is reduced to metal by heating with charcoal.
Uses of Cobalt
In the United States, superalloys account for 45 percent of cobalt use. Other uses include magnetic alloys, cemented carbides, catalysts, driers in paint, pigments, steel, welding materials, and other alloys. One isotope, cobalt 60, is important as a source of gamma rays. It is used in the medical field to treat malignant growths. The steel alnico, which also contains aluminum and nickel, is used to make permanent magnets that are twenty-five times as strong as ordinary steel magnets. In the ceramics industry, cobalt is used as a pigment to produce a better white by counterbalancing the yellow tint caused by iron impurities.
Bibliography
Greenwood, N. N., and A. Earnshaw. “Cobalt, Rhodium, and Iridium.” In Chemistry of the Elements. 2d ed. Boston: Butterworth-Heinemann, 1997.
Hampel, Clifford A., ed. The Encyclopedia of the Chemical Elements. New York: Reinhold, 1968.
Kim, James H., Herman J. Gibb, and Paul D. Howe. Cobalt and Inorganic Cobalt Compounds. Geneva, Switzerland: World Health Organization, 2006.
Leopold, Ellen. “The Rise of Radioactive Cobalt.” In Under the Radar: Cancer and the Cold War. New Brunswick, N.J.: Rutgers University Press, 2009.
Mertz, Walter, ed. Trace Elements in Human and Animal Nutrition. 5th ed. 2 vols. Orlando, Fla.: Academic Press, 1986-1987.
Ochiai, Ei-ichiro. General Principles of Biochemistry of the Elements. Vol. 7 in Biochemistry of the Elements. New York: Plenum Press, 1987.
Silva, J. J. R. Fraústo da, and R. J. P. Williams. “Nickel and Cobalt: Remnants of Life?” In The Biological Chemistry of the Elements: The Inorganic Chemistry of Life. 2d ed. New York: Oxford University Press, 2001.
Syracuse Research Corporation. Toxicological Profile for Cobalt. Atlanta, Ga.: U.S. Dept. of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, 2004.
Weeks, Mary Elvira. Discovery of the Elements. 7th ed. New material added by Henry M. Leicester. Easton, Pa.: Journal of Chemical Education, 1968.
Natural Resources Canada.
U.S. Geological Survey.